1. Field of the Invention
This invention relates to a method and an apparatus for producing a dough product from starch containing ingredients of cellular structure to obtain a product, preferably containing at least 50 percent starch material. The starch containing raw material exhibits a cellular structure, and in many cases, but not in all, the end product can show a cellular structure too; the invention is, however not restricted to such an end product.
2. State of the Art
U.S. Pat. No. 4,055,681 discloses a method for producing an expanded dry pet food from starch containing material. Downstream an extruder, there is a bent tube-like hollow attachment which has a jacket to be heated by steam to cool a dough-like product at 200.degree. F. to 300.degree. F. The bending(s) of the tube, however, prevent a uniform flow of the material so that it cannot be shaped in a single procedure. In addition, a belt is necessary to spread the relatively liquid dough over its surface, after which the flat dough is cut into strips or plates to be cut into granules in an additional step.
U.S. Pat. No. 4,790,996 discloses an extrusion tube cooker which comprises a straight tube attached to the end of an extruder, such as a twin-screw extruder. A die at the end of the tube has a plurality of shaping openings, the cross-section of which is, obviously, smaller than the inner cross-section of the tube. The problem with such an extrusion tube cooker is how to fill the whole inner cross-section of the tube. While the final product is withdrawn from the die's openings by means of rollers or the like, a non-uniformly filled tube produces a completely gelatinized product of poor uniformity. Here also, additional means are necessary to accomplish final shaping, for example a comminution mill, grating rolls, briquetting means, pelletizers or the like. Moreover, the gelatinized product, when used as a snack food, cannot maintain its "body" as soon is contacts liquids, such as milk; being of a poor "bowl life" (cf. "Extruded Cereals and Snacks", Massoud Kazemzadeh, Buhler Inc., Minneapolis, 1993) it becomes an undefined squash which gives a less than agreeable feeling in the mouth.